Low multiplicity pion proton interactions at 5.0 and 11.5 Gev/c

Abstract

The interactions of positive pi-mesons in a hydrogen bubble chamber have been studied at incident momenta of 5.0 Gev/c and 11.5 Gev/c. The various channel reactions have been separated by the processes of scanning, measuring, and computer analysis. The total cross: sections are 26.5mb and 24.9mb at 5 Gev/c and 11.5 Gev/c respectively. The elastic channel has been found to exhibit an energy independent optical diffraction character in that the slopes of the very forward differential cross sections remain in the region of 7-9 Gev(^-2) over a large energy range. The inelastic reaction π(^+)p→π(^+)pπ(^o) shows the production of the N*(^++) (1236) and p(^+)(760) resonances in highly peripheral interactions. However, the fraction of such quasi-two-body reactions falls sharply from 24.8% at 5 Gev/c to 8.25% at 11.5 Gev/c. The p+(760) differential cross section and decay density matrix elements are in reasonable agreement with absorptive peripheral model predictions for one pion exchange, whereas the N*(^++)(1236) differential cross section disagrees with the model prediction for ρ exchange. However, the Regge pole model for ρ trajectory exchange gives a reasonable fit to the N*(^++) differential cross section at both energies. The slopes of the differential cross sections for N*(^++) and p(^+) production have been found to have values in the range 7-9 Gev(^-2) of the same order as that for elastic scattering, indicating, rather qualitatively, an optical diffraction nature for the reactions. The NO FIT reactions (with more than one neutral particle in the final state) show production of the ηº(550) and fº(1260) mesons, and also the quasi-two-body production of N*(^++)ηº and N*(^++)fº. There is evidence for the A2(1300) meson and possibly the A(_3)(1640) meson, although it is only observed at 5 Gev/c.